1. Field of the Invention
The present invention relates to position sensitive detectors and distance measuring apparatus using them.
2. Related Background Art
As distance measuring apparatus for measuring a distance to a measured object, there are well-known distance measuring apparatus provided with a light source and a position sensitive detector. Such distance measuring apparatus are constructed on the basis of the triangulation principle and arranged to measure the distance to the measured object, based on a position where light having been projected from the light source and then reflected at the measured object is incident to a photosensitve surface of the position sensitive detector. Specifically, the position where the light is incident to the photosensitve surface of the position sensitive detector varies in a base line direction according to the distance to the measured object. Accordingly, the distance to the measured object can be measured by detecting the incidence position of the light on the photosensitve surface.
A well-known position sensitive detector used in the above distance measuring apparatus is constructed in such structure that a pair of signal extracting electrodes are provided at two ends of a conductive trunk region extending in the base line direction, a plurality of conductive branch regions extending perpendicular to the trunk region (or the base line direction) are arranged in the base line direction, and each of the branch regions is electrically connected to the trunk region. In the position sensitive detector of this structure, charges (carriers) generated with incidence of light flow into the neighboring branch regions and then propagate in the direction perpendicular to the base line direction in the branch regions to flow into the trunk region. After that, the charges are split there in inverse proportion to resistances from the inflow position to the both ends of the trunk region and the charges thus split propagate in the trunk region to be outputted from the respective signal extracting electrodes. Therefore, the incidence position of light on the photosensitve surface can be detected by comparing output currents from the two signal extracting electrodes.
The above distance measuring apparatus, however, had the following problem. Specifically, in the case of the distance measuring apparatus constructed to project the light from the light source to the measured object and detect the reflected light from the measured object, there can occur such a phenomenon that part of the light projected from the light source deviates from the measured object (which will be referred to hereinafter as spot chipping). With the spot chipping, the position sensitive detector can detect the reflected light of only part of the light projected from the light source and can cause a measurement error of the distance to the measured object in certain cases.
Particularly, since the incidence position of the light onto the photosensitve surface of the position sensitive detector varies according to the distance to the measured object in the base line direction, the measurement error will be large if the spot chipping occurs in the base line direction. Namely, in use of the above conventional position sensitive detector, the carriers generated with incidence of light propagate in the direction perpendicular to the base line direction in the branch regions to flow into the trunk region, and thus a deviation of the center of gravity in the base line direction of the incident light due to the spot chipping leads to a measurement error as it is.
In contrast with it, for example, the distance measuring apparatus disclosed in Japanese Patent Application Laid-Open No. H05-164552 is arranged to project spot light of asymmetric shape with respect to the base line direction and receive the spot light by triple photodetective elements, thereby correcting the measurement error due to the spot chipping.
Such distance measuring apparatus, however, needs to use the light emitting device for projecting the spot light of asymmetric shape and the triple light receiving elements and each of the elements or the distance measuring apparatus itself becomes complicated and large in scale and is difficult to make up at low cost. An object of the present invention is to provide distance measuring apparatus with a reduced measurement error and position sensitive detectors used therein.
A position sensitive detector according to the present invention is a position sensitive detector in which currents outputted from two ends of a conductive trunk region vary according to a position of incidence of light on a photosensitve surface comprising a plurality of conductive branch regions extending from the trunk region, wherein the branch regions extend substantially obliquely relative to a position detection direction. When the detector is incorporated in the distance measuring apparatus, the position detection direction is coincident with the base line direction. A minimum of an angle between the extending direction of the branch regions and the position detection direction is preferably not more than 85xc2x0, more preferably not less than 30xc2x0, and still more preferably approximately 45xc2x0. The term xe2x80x9capproximatelyxe2x80x9d herein means variation of less than xc2x15%. Each of the branch regions preferably has a substantially equal width along the extending direction, the extending direction of each of the branch regions is preferably constant in the photosensitve surface, and it is preferable that a luminous shape of the incident light to the position sensitive detector be a rectangle and that the longitudinal direction of the rectangle be coincident with the extending direction of the branch regions. This incident light preferably has a size enough to simultaneously overlap with a plurality of branch regions. It is preferable that a pair of signal extracting electrodes be provided at two ends of the trunk region and that each of the pair of signal extracting electrodes be of a nearly triangular shape.
Since the above position sensitive detector reduces the possibility of causing the measurement error due to the spot chipping, a distance measuring apparatus with high accuracy and with a reduced measurement error can be provided when the detector is incorporated therein.